WO2007033720A1

WO2007033720A1 - Rubber mixture and tires

Info

Publication number: WO2007033720A1
Application number: PCT/EP2006/007236
Authority: WO
Inventors: Boris Mergell; Carla Recker
Original assignee: Continental Aktiengesellschaft
Priority date: 2005-09-21
Filing date: 2006-07-22
Publication date: 2007-03-29
Also published as: ATE434641T1; DE102005044998A1; EP1928944B1; EP1928944A1; DE502006004084D1

Abstract

The invention relates to a sulfur cross-linkable rubber mixture that comprises, for the purpose of imparting it with improved hardness, improved dynamic storage modulus E' and reduced loss factor tan d at 60 °C, at least one diene rubber, 0.1-10 phr of at least one dithiophosphate accelerator and 0.3 - 5 phr tin 2-ethylhexanoate.

Description

Continental Corporation

description

Rubber compound and tires

The invention relates to a sulfur-crosslinkable rubber mixture containing at least one diene rubber and at least one accelerator. Further, the invention relates to tires, in particular pneumatic vehicle tires, whose treads are based at least in part on the sulfur vulcanized rubber composition.

In order to influence the mixing and vulcanizate properties, a wide variety of additives are added to the mixtures and / or special polymers are used. Fillers which may be mentioned by way of example at this point are fillers (for example carbon black), plasticizers, aging inhibitors and sulfur, accelerator and activator crosslinking systems. If a property is improved by varying the mixture, this often results in a deterioration of another property, so that certain conflicting goals exist. For vehicle tire tread mixtures, for example, such trade-offs exist in terms of rolling resistance and handling, as well as wet grip and rolling resistance. It is therefore desirable to solve these conflicting goals by varying the composition of the mixture and to achieve an improved level of the usually contrary behaving properties.

An important group of additives that has an influence on the vulcanization rate and the physical properties of vulcanizates is the group of vulcanization accelerators. For the vulcanization of sulfur-crosslinkable rubber mixtures, the following vulcanization accelerator groups are primarily selected: mercapto accelerator (eg 2-mercaptobenzothiazole), sulfenamide accelerator (eg benzothiazyl-2-cyclohexylsulfenamide (CBS)), thiuram accelerator (e.g. Tetramethyl thiuram disulfide (TMTD)), dithiocarbamate accelerators (eg zinc dibenzyldithiocarbamate) and guanidine accelerators (eg N ₃ N ' ₎ . Diphenylguanidine (DPG)). The accelerators can also be used in combination with each other, which can result in synergistic effects. Further, for the vulcanization of ethylene-propylene-diene copolymers (EPDM), the use of dithiophosphate accelerators (eg, zinc dibutyl dithiophosphate (ZDBP)) is common. For diene rubber mixtures, dithiophosphate accelerators are used in combination with mercapto and / or sulfenamide accelerators. In EP 0 767 205 A1, metal alkyldithiophosphates in combination with dithiophosphoric acid polysulfides are also proposed for the acceleration of sulfur-crosslinkable natural rubber mixtures with a reduced tendency to reverse.

It is customary with a rubber mixture for sulfur crosslinking with

Vulkanisationsbeschleunigern acceleration activators, such. As zinc oxide in combination with fatty acids, usually add stearic acid. The sulfur is then activated by complex formation for vulcanization. As an activator for natural rubber mixture is also on the market zinc 2-ethylhexanoate, z. B. under the name Struktol ^® ZEH from the company Schill + Seilacher, Germany, available, which in addition to a strong activation effect on the vulcanization also increases the crosslinking density and the reversion resistance. In addition, zinc 2-ethylhexanoate is said to reduce stress relaxation, improve dynamic properties and make-up tack. Zinc 2-ethylhexanoate can replace all or part of the stearic acid activator.

It is an object of the present invention to provide rubber compounds, in particular for the treads of vehicle tires, whose vulcanizates are accompanied by an increased hardness and an increased dynamic storage modulus E '

55 ° C at the same time only slightly reduced loss factor tan δ at 0 ⁰ C and reduced loss factor tan δ at 60 ⁰ C distinguished.

The hardness at room temperature and the dynamic storage modulus E 'at 55 ° C are considered in the tire industry for tire tread compounds as a measure of handling, a higher hardness is accompanied by improved handling. The loss factor tan δ at 0 ° C is a measure of wet braking, with a high loss factor tan δ at 0 ° C in resulting in improved wet braking. The loss factor tan δ at 60 ° C, on the other hand, is a measure of the rolling resistance. A reduction in the loss factor tan δ at 60 ⁰ C results in an improvement (reduction) of the rolling resistance.

When the rubber composition having the above characteristics is used for the tread of a pneumatic vehicle tire, the higher hardness and the increased dynamic storage modulus E 'result in improved handling performance, while the wet grip deteriorates only slightly and the rolling resistance is reduced.

This object is achieved according to the invention in that the rubber mixture

at least one diene rubber,

- 0.1 - 10 phr of at least one dithiophosphate accelerator and

Contains 0.3 to 5 phr of zinc 2-ethylhexanoate.

The term phr (parts per hundred parts of rubber by weight) used in this document is the quantity used in the rubber industry for mixture formulations. The dosage of the parts by weight of the individual substances is always based on 100 parts by weight of the total mass of all the rubbers present in the mixture.

Surprisingly, it has been found that by the specific combination of 0.1-10 phr of at least one dithiophosphate accelerator with 0.3-5 phr of zinc 2-ethylhexanoate in sulfur-crosslinkable rubber mixtures containing at least one diene rubber, the hardness and the dynamic storage modulus E 'and the loss factor tan δ at 60 ° C can be reduced without the loss factor tan δ at O ⁰ C drops sharply. Dithiophosphate accelerator as the soluble accelerator and the zinc 2-ethylhexanoate appear to provide very high uniformity in spatial network distribution, making the network as a whole tighter, ie harder, and reducing the viscous areas, resulting in reduced hysteresis , In the case of vehicle tires with the mixtures according to the invention as tread, the otherwise oppositely behaving properties of handling and rolling resistance as well as handling and wet grip can be decoupled from one another.

The rubber mixtures according to the invention additionally have the advantage that they show markedly shorter heating times with better scorch safety (scorch safety, prevention of premature scorching). The abrasion behavior of the Mischungsvulkanisate is also improved, d. H. the abrasion is reduced.

The sulfur crosslinkable rubber mixture contains at least one diene rubber. The diene rubbers include all rubbers having an unsaturated carbon chain derived at least in part from conjugated dienes. Particularly preferred is when the diene rubber or diene rubbers is selected from the group consisting of natural rubber (NR), synthetic polyisoprene (IR), polybutadiene (BR), styrene-butadiene copolymer (SBR) and acrylonitrile-butadiene- Rubber (NBR). These

Diene elastomers work well with the rubber composition according to the invention and give good tire properties in the vulcanized tires.

The rubber mixture may contain polyisoprene (IR, NR) as the diene rubber. These may be both cis-1,4-polyisoprene and 3,4-polyisoprene. However, preference is given to the use of cis-1,4-polyisoprenes having a cis-1,4-content of> 90% by weight. First, such a polyisoprene can be obtained by stereospecific polymerization in solution with Ziegler-Natta catalysts or using finely divided lithium alkyls. On the other hand, natural rubber (NR) is such an iron-1,4-polyisoprene, the cis-1,4-content in natural rubber is greater than 99% by weight.

If the rubber mixture contains polybutadiene (BR) as the diene rubber, these may be both 1,4-vinyl and vinyl polybutadiene (10-90% by weight vinyl content). Cis-1,4-polybutadiene with a cis-l, 4-portion greater than 90 wt .-% may, for. By solution polymerization in the presence of rare earth type catalysts. The styrene-butadiene copolymer may be a solution-polymerized styrene-butadiene copolymer (S-SBR) having a styrene content, based on the polymer, of about 10 to 45% by weight and a vinyl content (content of 1.2 bound butadiene, based on the total polymer) of from 10 to 70% by weight, which can be prepared, for example, using lithium alkyls in organic solvent. The S-SBR can also be coupled and end-group modified. However, it is also possible to use emulsion-polymerized styrene-butadiene copolymer (E-SBR) and mixtures of E-SBR and S-SBR. The styrene content of the E-SBR is about 15 to 50% by weight, and the types known in the art obtained by copolymerization of styrene and 1,3-butadiene in aqueous emulsion can be used.

In addition to the diene rubbers mentioned, however, the mixture may also contain other types of rubber, such as. Styrene-isoprene-butadiene terpolymer, butyl rubber, halobutyl rubber or ethylene-propylene-diene rubber (EPDM).

The rubber mixture according to the invention contains 0.1-10 phr, preferably 0.5-7 phr, more preferably 1-5 phr, of at least one dithiophosphate accelerator. It is also possible to use several dithiophosphate accelerators in the mixture.

As a dithiophosphate accelerator z. B. dodecylammonium diisooctyldithiophosphat be used. However, metal alkyldithiophosphates are preferably used. As particularly effective in view of the improved vulcanizate properties have zinc alkyldithiophosphate, z. As zinc dibutyl dithiophosphate, zinc isobutyl isooctyl dithiophosphate and zinc diisooctyldithiophosphat proven.

The mixture according to the invention also contains 0.3-5 phr, preferably 0.75-4 phr, more preferably 1.1-3 phr, zinc 2-ethylhexanoate. The zinc 2-ethylhexanoate may be in the form of market-available on Struktol ^® ZEH or Struktol ^® ZEH-DL (zinc 2-ethylhexanoate silica), both of which are used by the company Schill + Seilacher, Germany.

The rubber mixture may contain as filler at least carbon black and / or silica. The usable carbon blacks preferably have the following characteristics: DBP number (according to ASTM D 2414) 90 to 200 ml / 100 g, CTAB number (according to ASTM D 3765) 80 to 170 m ² / g and iodine adsorption number (according to ASTM D 1510) 10 to 250 g / kg. The silicas may be the silicas known to those skilled in the art which are suitable as a filler for tire rubber mixtures. However, it is particularly preferred if a finely divided, precipitated silica is used which has a nitrogen surface area (BET surface area) (according to DIN 66131 and 66132) of 35 to 350 m ² / g, preferably 145 to 270 m ² / g and a CTAB surface area (according to ASTM D 3765) of from 30 to 350 m ² / g, preferably from 120 to 285 m ² / g. Such silicas lead z. B. in rubber mixtures for tire tread to particularly good physical properties of the vulcanizates. In addition, advantages in compounding processing can result from a reduction in mixing time with consistent product properties leading to improved productivity. As silicas can thus z. B. both those of the type VN3 (trade name) from Degussa and highly dispersible silicas, so-called HD silicas (eg Ultrasil 7000 from Degussa) are used. Also known as HDRS types (high dispersible reactive silica) can be used.

To improve the processability and to attach the silica and other optional polar fillers to the diene rubber silane coupling agents can be used in rubber mixtures. The silane coupling agents react with the superficial silanol groups of the silica or other polar groups during the mixing of the rubber or the rubber mixture (in situ) or even before the addition of the filler to the rubber in the sense of a pretreatment (pre-modification). All silane coupling agents known to those skilled in the art for use in rubber compounds can be used as silane coupling agents. Such known from the prior art coupling agents are bifunctional organosilanes having on the silicon atom at least one alkoxy, cycloalkoxy or phenoxy group as a leaving group and have as other functionality a group which may optionally undergo a chemical reaction with the double bonds of the polymer after cleavage , In the latter group may be z. For example, they may be the following chemical groups: - SCN, -SH, -NH ₂ or -S _x - (with x = 2-8). Thus, as silane coupling agents z. B. 3-mercaptopropyltriethoxysilane, 3-thiocyanato-propyltrimethoxysilane or 3,3'-bis (triethoxysilylpropyl) polysulfides having 2 to 8 sulfur atoms, such as. For example, 3,3'-bis (triethoxysilylpropyl) tetrasulfide (TESPT), the corresponding disulfide or mixtures of the sulfides having 1 to 8 sulfur atoms with different contents of the various sulfides are used. TESPT can be added, for example, as a mixture with carbon black (trade name X50S from Degussa). It can be called silane. Kupplungsagenzien also blocked mercaptosilanes are used.

The silane coupling agents are used in amounts of from 0.2 to 30 parts by weight, preferably from 1 to 15 parts by weight, based on 100 parts by weight of filler, in particular silica, since optimum bonding of the filler to the rubber (s) can then take place.

The rubber composition may also contain other fillers, such as

Alumosilicates, aluminum hydroxide, phyllosilicates, chalk, starch, magnesium oxide, titanium dioxide, rubber gels, etc. in any combination.

The rubber mixture can in addition to the substances mentioned other additives such. Plasticizers (e.g., aromatic, naphthenic or paraffinic mineral oil plasticizers, MES (mild extraction solvates), TDAE (treated distillate aromatic extract), RAE (residual aromatic extract), rapeseed oil, or liquid polymers, for example, liquid butadiene-styrene random). Copolymers or liquid polybutadiene).

Furthermore, the rubber mixture according to the invention may contain customary additives in customary parts by weight. These additives include anti-aging agents, such as. N-phenyl-N '- (1,3-dimethylbutyl) -p-phenylenediamine (6PPD), N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), 2,2,4-trimethyl-1, 2-dihydroquinoline (TMQ) and other substances, as described, for example, in J. Schnetger, Encyclopedia of Rubber Technology,

2nd edition, Hüthig book Verlag, Heidelberg, 1991, pp. 42-48 are known, activators such. As zinc oxide and fatty acids (eg., Stearic acid), waxes, resins and Mastikationshilfsmittel such. B. 2,2'-Dibenzamidodiphenyldisulfid (DBD). The vulcanization is carried out in the presence of sulfur or sulfur donors, with some sulfur donors can also act as a vulcanization accelerator. Sulfur or sulfur donors are added together with the accelerators in the last mixing step in the amounts customary by the skilled person (0.4 to 6 phr, sulfur preferably in amounts of 1.5 to 2.5 phr) of the rubber mixture.

According to a preferred development of the invention, the rubber mixture contains sufficient processing safety and low vulcanization

Reverse tendency in addition to at least one dithiophosphate accelerator at least one further vulcanization accelerator selected from the group consisting of mercapto accelerators (eg 2-mercaptobenzothiazole), sulfenamide accelerators (eg., Benzothiazyl-2-cyclohexylsulfenamid (CBS)), thiuram Accelerators (eg Tetramethylthiuram Disulfide (TMTD), Dithiocarbamate Accelerators (eg.

Zinc dibenzyldithiocarbamate) and guanidine accelerators (e.g., N, N'-diphenylguanidine (DPG)). The or the further vulcanization accelerators are preferably used in amounts of 0.5 to 7 phr.

If the dithiophosphate accelerator is used in combination with other accelerators, the conventional accelerator can be exchanged molar compared to the usual rubber mixture without dithiophosphate accelerator. It is then preferably 25 to 75 mol% of the conventional accelerator replaced by the dithiophosphate accelerator.

The rubber mixture may also contain conventional vulcanization retarders in conventional amounts.

The preparation of the rubber mixture according to the invention is carried out in a conventional manner, wherein initially generally a base mixture containing all constituents except the vulcanization system (sulfur, possibly sulfur donor, accelerator and optionally retarder), in one or more mixing stage (s) is prepared and then produced by adding the vulcanization system, the finished mixture. Subsequently, the mixture is further processed, for. B. brought by an extrusion process, and in the appropriate form.

The rubber mixture can, for. B. for different tire components, for example as a mixture in the core and / or belt area or as a crescent-shaped runflat insert in the sidewall area. However, the mixture is preferred as

Tread used and brought for this purpose in the form of a tread. A tread blending blank produced in this way is applied during the production of the green tire, in particular the pneumatic vehicle tire blank, as is known. However, the tread may also be wound onto a green tire, which already contains all the tire parts except the tread, in the form of a narrow rubber compound strip.

After vulcanization, the vulcanizates have a high hardness and a high dynamic storage modulus E 'and a reduced loss factor tan δ at 60 ° C. Pneumatic vehicle tires with a tread of such a mixture have good handling with reduced rolling resistance.

The invention will now be explained in more detail with reference to comparative and exemplary embodiments, which are summarized in Tables 1.

For all of the mixture examples shown in Table 1, the amounts given are parts by weight based on 100 parts by weight of total rubber (phr). The comparison mixtures are marked V, the mixture according to the invention is marked E. The mixtures in Table 1 differ only in stearic acid or zinc 2-ethylhexanoate and the vulcanization accelerators used, the remaining mixture components remain unchanged.

Mixture preparation was carried out under standard conditions in two stages in a laboratory tangential mixer. The conversion times until reaching the relative degrees of crosslinking of 5 and 90% (t ₅ , tgo) were determined via a rotorless vulcameter (MDR = Moving Disc Rheometer) in accordance with DIN 53 529. From all mixtures were

Test specimens produced by optimal vulcanization under pressure at 160 ⁰ C and determined with these specimens for the rubber industry typical material properties with the test methods given below. Shore A hardness at room temperature and 70 ^° C. according to DIN 53 505

• Rebound resilience at room temperature and 70 ⁰ C according to DIN 53 512

Tensile strength at room temperature in accordance with DIN 53 504

• Elongation at room temperature according to DIN 53 504 • Tension values at 50, 100, 200 and 300% elongation at room temperature according to

DIN 53 504

• Breaking energy density determined in the tensile test according to DIN 53 504, wherein the fracture energy density is the work required up to breakage, based on the volume of the sample. • Dynamic Young's modulus E 'at 8% dynamic deformation amplitude according to DIN 53 513 from constant temperature measurement of 55 ⁰ C and a pre-deformation of 20% in compression with 10 Hz dynamic deformation frequency

• Loss factor tan δ at 0 and 60 ° C according to DIN 53 513 from measurement with constant deformation amplitude of 0.2% at 10% pre - deformation in compression with 10

Hz dynamic deformation frequency

• Attrition at room temperature according to DIN 53516

Table 1

^a high-cis polybutadiene ^b solution polymerized styrene-butadiene copolymer, styrene content: end-group 21 wt .-%, vinyl content 61%, and tin coupled ^c Ultrasil ^® VN3, Degussa, Germany ^d Silquest ^® A-1589, OSi, USA ^c Struktol ^® ZEH 75 (ZEH on silica carrier, 75% ZEH, 25% silica) Firma

Schill + Seilacher, Germany ^f Zinc diisooctyldithiophosphate, Rhenogran ^® ZDT-50 with polymer binder EPDM / EVA, 50% starting material, Rheinchemie, Germany

From Table 1 it can be seen that the sole addition of zinc 2-ethylhexanoate in exchange for stearic acid (mixture 2 (V)) causes only very slight changes in the physical characteristics of the vulcanizates compared to mixture 1 (V). Only the turnover time until reaching the relative degree of crosslinking of 5% t ₅ is slightly increased, which provides improved scorch safety, and the turnover time until the relative degree of crosslinking of 90% t ₉₀ is slightly reduced. The partial replacement of the accelerator CBS by zinc dialkyldithiophosphate as accelerator according to mixture 3 (V) results in the mixing vulcanizates with improved scorch safety and significantly shortened vulcanization time in a slightly higher hardness, a higher dynamic storage modulus E ', a greatly reduced loss factor tan δ at 0 ⁰ C, a decreased loss factor tan δ at 60 ° C and increased abrasion. Using such a tire tread compound, these property changes would increase the trade-off between wet grip and rolling resistance.

Only the special combination of zinc dialkyldithiophosphate with zinc 2-ethylhexanoate (mixture 4 (E)) surprisingly leads to an even higher hardness and an even higher dynamic storage modulus E 'of the mixed vulcanizates with simultaneously reduced loss factor tan δ at 60 ° C. This means that in a tire with such a mixture as a tread, both the handling and the rolling resistance are improved. At the same time, wet braking remains at a high level (loss factor tan δ still high at 0 ° C). The difference between loss factor tan δ at 0 ° C and loss factor tan δ at 60 ° C is large. In comparison to the blends 2 (V) and 3 (V), both the conflict between handling and rolling resistance and between wet grip and rolling resistance can be solved. Also, the abrasion is improved again in the mixture 4 (E). In addition, the scorch safety is increased and the short turnaround time until reaching the relative degree of crosslinking of 90%. ₉₀ allows even shorter heating times.

Claims

claims

A sulfur-crosslinkable rubber mixture comprising at least one diene rubber, 0.1-10 phr (parts by weight based on 100 parts by weight of rubber) of at least one dithiophosphate accelerator and 0.3-5 phr of zinc 2-ethylhexanoate.

2. Rubber mixture according to claim 1, characterized in that it contains 0.5 to 7 phr, preferably 1 to 5 phr, of at least one dithiophosphate accelerator.

3. Rubber mixture according to claim 1 or 2, characterized in that the dithiophosphate accelerator is a Metallalkyldithiophosphat.

4. rubber mixture according to claim 3, characterized in that the dithiophosphate accelerator is a Zinkalkyldithiophosphat.

5. Rubber mixture according to at least one of the preceding claims, characterized in that it contains 0.75-4 phr, preferably 1.1-3 phr, zinc 2-ethylhexanoate.

6. rubber mixture according to at least one of the preceding claims, characterized in that they at least one further vulcanization accelerator selected in addition to at least one dithiophosphate accelerator selected from the group consisting of mercapto accelerators, sulfenamide accelerators, thiuram

Accelerators, dithiocarbamate accelerators and guanidine accelerators.

7. Rubber mixture according to claim 6, characterized in that it contains 0.5 to 7 phr of the or more vulcanization accelerator (s).

8. Tires, in particular pneumatic vehicle tires, whose tread is based at least in part on a sulfur vulcanized rubber composition according to one of claims 1 to 7.